Multi-rod bone attachment member

ABSTRACT

A fixation element for use in orthopedic surgery, particularly spinal surgery is disclosed. The fixation element is capable of being screwed, hooked, or otherwise attached to a bone, and is configured to accommodate two or more rods or other elongated members. The head of the fixation elements thus has multiple places for positioning a rod, either vertically or horizontally spaced from each other.

BACKGROUND OF THE INVENTION

A variety of implants are known in the art for attaching an elongatedmember, e.g. an elongated bar or rod, to one or more bones for thepurpose of correcting deformity, promoting healing, or other therapeuticuses. Among such devices are those disclosed in U.S. Pat. No. 5,005,562to Cotrel, U.S. Pat. No. 5,797,911 to Sherman et al., and U.S. Pat. No.6,280,442 to Barker et al. In those devices, a U-shaped head is providedfor accommodating an orthopedic rod, such as that used in correctivespinal surgery. A threaded element or hook connects the U-shaped head toa bone portion, and a set screw locks the elongated rod within theU-shaped head.

SUMMARY OF THE INVENTION

In one embodiment, an apparatus is disclosed which comprises a one-piecehead portion having one or more channels, with the channels beingconfigured so that a plurality of elongated members (e.g. spinal rods)may be connected to the head via one or more of the channels. At leastone holder is connected to the head portion and holds at least one ofthe elongated members within their respective channels, and anattachment portion is provided connected to the head portion forconnecting the head portion to a bone. There may be two substantiallyparallel channels in the head portion, with the head portion beingsubstantially W-shaped. Such a pair of channels can have approximatelythe same width or radius, or one of the channels can have a width orradius larger than the other. A female thread can be formed in each ofsuch channels, with set screws provided as the holders. The attachmentportion may be integral with or may be movably connected with the headportion. If they are movably connected, the attachment portion may berotatably or multi-axially connected with the head portion.

Another embodiment of an apparatus according to the invention comprisesa head portion having first and second outer legs and at least one postbetween the legs, a first channel between the first leg and the post,and a second channel between the second leg and the post. A first threadis formed on the first leg and the post, and a second thread is formedon the second leg and the post. First and second set screws areprovided, with the first set screw adapted to be threaded in the firstthread to close the first channel, and the second set screw adapted tobe threaded in the second thread to close the second channel. A boneconnection portion is connected to the head portion, whereby theapparatus is connected to a bone. The apparatus can further comprise afirst elongated member, such as a spinal rod, such that at least aportion of the first elongated member occupies at least a portion of thefirst channel. The first set screw provides a clamping force to hold theelongated member with respect to the head portion. A second elongatedmember can also be provided such that at least a portion of the secondelongated member occupies at least a portion of the second channel inthe head portion, and the second set screw provides a clamping force tohold the second elongated member with respect to the head portion.

A method is also disclosed, comprising providing a bone-engagingapparatus having an upper head portion and at least one lower attachmentportion, with the head portion having a plurality of channels forreceiving one or more elongated members; connecting the attachmentportion of the apparatus to a bone; inserting an elongated member intoone of the channels; and connecting a holder to said head portion tohold said elongated member in said channel. The holder connecting stepcan include threading a set screw into the channel into which theelongated member has been inserted until the set screw exerts a clampingforce on said elongated member sufficient to lock it with respect to thehead portion. The method may further include inserting a secondelongated member into one of the channels. The channel into which thesecond elongated member is inserted can be previously occupied orunoccupied by an elongated member. An additional holder may be provided,if necessary, for the second elongated member. For example, a set screwmay be threaded into the channel into which the second elongated memberhas been inserted until it exerts a clamping force on the secondelongated member. The method may also include adjusting the bone priorto insertion of the first elongated member, and further adjustment ofthe bone prior to insertion of the second elongated member. The relativeposition of the attachment portion and the head portion may be adjustedprior to a time when the elongated member(s) are locked with respect tothe apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a first embodiment of a bonefixation clement according to the invention.

FIG. 2 is a side view of the embodiment shown in FIG. 1.

FIG. 3 is a cross-sectional view taken along the lines 3-3 and viewed inthe direction of the arrows of the embodiment shown in FIG. 1.

FIG. 4 is a partial cross-sectional view of a further embodiment of abone fixation element according to the invention.

FIG. 5 is a partial cross-sectional view of another embodiment of a bonefixation element according to the invention.

FIG. 6 is a partial cross-sectional view of yet another embodiment of abone fixation element according to the invention.

FIG. 7 is a partial cross-sectional view of another embodiment of a bonefixation element according to the invention.

FIG. 8 is a partial cross-sectional view of a still further embodimentof a bone fixation element according to the invention.

FIG. 9 is a partial cross-sectional view of another embodiment of a bonefixation element according to the invention.

FIG. 10 is a side view of yet another embodiment of a bone fixationelement according to the invention.

FIG. 11 is a side view of another embodiment of a bone fixation elementaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated, as would normally occur to one skilled in the art to whichthe invention relates.

Referring now generally to FIG. 1, there is shown one embodiment of afixation element 10 according to the present invention. In thatembodiment, fixation element 10 includes a head portion 12 and anattachment portion 14. Although fixation element 10 is depicted as abone screw, with a threaded attachment portion 14, one of ordinary skillin this art will appreciate that threaded attachment portion 14 could bereplaced with a U-shaped or L-shaped hook element adapted to be fixed toa part of a bone, such as a pedicle or spinous process of a vertebra, orwith another device allowing connection to a bone.

In the embodiment shown in FIG. 1, head portion 12 is substantially inthe shape of a W, having two outer legs or legs 16, 18, and a post 20between legs 16, 18. Leg 16 and post 20 form a first channel 22, and leg18 and post 20 form a second channel 24. Channels 22 and 24 arepreferably substantially straight and substantially parallel, and have alower surface 26, 28, which may be curved or form a part of a cylinder.Channels 22 and 24 are sized and shaped to accommodate a rod or otherelongated element R. In one particular embodiment, channels 22 and 24are sized to accommodate rods of the same size, as for example where theradius of curvature of surfaces 26 and 28 are equal.

Channels 22 and 24 are bounded by wall sections 32 and 34, and 36 and38, respectively. Wall section 32 is an inner part of leg 16, wallsections 34 and 36 form sides of post 20, and wall section 38 is aninner part of leg 18. Wall sections 32 and 34 include a female thread40, and wall sections 36 and 38 include a female thread 42. Threads 40and 42 are adapted to accommodate set screws, such as that denoted as 44in FIG. 1, and threads 40, 42 and set screws 44 arc holders that closechannel 22 and hold or lock a rod or other elongated member therein. Thesize of the set screw needed to close channel 22 will, of course, dependon the characteristics of thread 40, just as thread 42 will determinethe size of the set screw for channel 24. If an alternative holder isdesired (such as a cam lock, a sliding member, a cap or nut with threadsor a bayonet-lock), threads 40 and/or 42 may be altered, removed, orreplaced with other features (e.g. grooves, external threads or thelike) that permit connection to such holders.

Further, in the above-described embodiment it is preferred that there bea set screw 44 and compatible threads (e.g. threads 40, 42) for eachchannel, i.e. a first set screw 44 for channel 22 and a second set screw44 for channel 24. It would be possible to use one or more holders ofanother type, e.g. caps or nuts, to contain or lock multiple rods orother elongated members within their specific channels. For example, acap or nut that surrounded and connected to legs 16 and 18 of headportion 12 would close both channels 22 and 24 and keep elongatedmember(s) therein. In that case, there would be one holder to hold oneor more elongated members within their respective channels, whereas withset screws several holders (i.e. set screws) may be needed to holdseveral elongated members within their respective channels. It will alsobe observed that not all holders elements need be the same, but thatscrews, nuts, caps, sliders or cams can be combined for use with a givenhead portion.

In the embodiment of fixation member 10 in which channels 22 and 24accommodate rods of the same size, the widths of the channels (i.e. therespective distances between walls 32 and 34 and between walls 36 and38) will be approximately equal, and may accommodate identical setscrews. On the outsides of legs 16 and 18 are found indentations 46 and48, respectively. Indentations 46 and 48 are adapted to accommodate aholding or twisting tool, such as a screwdriver. In one embodiment,indentations 46 and 48 are substantially circular, and may have aslightly tapered opening, so that a projection on a gripping or screwingtool that has a circular or other shape can easily be inserted intoindentations 46 and 48.

In the embodiment of FIG. 1, attachment portion 14 may be formedintegrally with head portion 12, or may be made separately from headportion 12 and fixedly attached to head portion 12 after manufacture.Attachment portion 14 is a threaded member in the illustratedembodiment, having threads 50 adapted for insertion into a bone.Attachment portion 14 is illustrated as having a flattened end 52, butit will be understood that end 52 may also be pointed and/orself-tapping. Fixation element 10 may also be cannulated, i.e. having anaperture 54 extending from end 52 of attachment portion 14 to the top ofpost 20 of head portion 12. The embodiment of FIG. 1 also showsattachment portion 14 along a medial axis (i.e. equidistant from theoutside edges of legs 16 and 18) of head portion 12. As shown anddescribed below with respect to other embodiments, attachment portion 14may be placed to one side of a medial axis, for example directly beneathone of channels 22 and 24.

In use, access to an orthopedic surgical site is obtained in a knownmanner. A drill or similar device is used to make a hole in a bone. Forconvenience, use of fixation element 10 will be described with respectto spinal surgery, although it is understood that the present inventionmay be used with other bony tissue or another surgical site. After ahole is drilled in a vertebra, attachment portion 14 of fixation element10 is inserted, and fixation element 10 is rotated so that fixationelement 10 is screwed into the hole. The surgeon continues turningfixation element 10 until it is in a desired position, e.g. head portion12 is at a desired height from the surface of the vertebra, and channels22 and 24 are oriented as the surgeon desires for a rod. When used inspinal surgery, commonly fixation element 10 will be threaded into thebone until most or all of thread 50 is within the bone, and channels 22and 24 are oriented substantially along the spinal column or along adesired orientation of one or more spinal segments.

One or more rods or other elongated members can then be connected tofixation element 10. As shown in FIG. 1, rod R is placed in channel 22,and set screw 44 is screwed into internal thread 40 to close channel 22and hold or lock rod R therein. Of course, rod R may also be placed inchannel 24, in substantially the same manner as described above. If tworods are used, one rod may be placed in each of channels 22 and 24 andheld or locked therein with set screws, as described above.

In a minimally-invasive procedure, access to the surgical site isavailable through one or more small openings through the skin and/orother soft tissues. Instruments suited to minimally-invasive proceduresare inserted through such an opening and moved to the surgical site,where the steps described above are performed. Although this inventioncan be used in a variety of surgical techniques, it has been found tohave significant application in minimally-invasive spinal surgery. Insuch procedures, it can be difficult to use screws or hooks thataccommodate only a single rod or other elongated member, because of therigidity of the corrective rod that must be implanted and because of therelative lack of mechanical advantage to adjust the spine when it is notexposed. Using the present invention, a surgeon can insert a screw orhook minimally-invasively, perform a degree of adjustment to the spineand connect a first rod that may be somewhat less rigid than is normallyused in corrective spinal surgery (e.g. scoliosis-correcting surgery).The first rod holds the affected spinal segment(s) sufficiently whileanother, more-rigid rod is prepared and the spine adjusted to its final,corrected position. The second rod is then inserted and locked into thescrews or hooks, and the surgery is completed. In some cases, it iscontemplated that use of yet additional rods or other elongated membersor additional spine-adjustment steps may be indicated or necessary, andthus screws or hooks that accommodate three or more rods come within thespirit of the invention.

Several other embodiments are described below. For convenience, featuresor aspects that are identical or similar in two or more embodimentsdisclosed herein are denoted in the description and drawings by numberssharing their last two digits.

An alternative embodiment of a fixation member 110 is depicted in FIG.4. Fixation element 110 is substantially the same as fixation member 10with the exception that fixation member 110 has one channel (e.g.channel 124) that will accommodate a rod larger than the other (e.g.channel 122) will accommodate. Lower surface 126 of channel 122 has asmaller radius than bottom surface 128 of channel 124, and the distancebetween walls 132 and 134 of channel 122 is smaller than the distancebetween walls 136 and 138 of channel 124. A smaller set screw or otherholding or locking element may be used in channel 122 compared to thatused in channel 124. In other respects, fixation element 110 isessentially the same as fixation element 10.

Fixation element 110 may be used where it is preferred to have two rodsof different diameters in a particular orthopedic construct. In thespinal surgical field, for example, it is common to reposition(distract, compress, rotate, or otherwise adjust relative location)vertebrae prior to or during implantation of a supporting or correctiveapparatus. Connecting a smaller, less-rigid rod to fixation element 110as described above will allow some holding or support of a spine thathas been adjusted, while still allowing the surgeon to readjust thespine and/or contour a larger, more-rigid rod for providing the mainsupport or correction to the spine.

Fixation element 110 may be placed in a vertebra as described above withrespect to fixation element 10. A first rod R1 of relatively smallerdiameter may be placed in channel 122, and held with a set screw 144.The surgeon can then perform additional or new repositioning proceduresif he or she chooses, and may bend the locked rod in the process. Whilethe relatively smaller rod R1 is holding the vertebra as desired, thesurgeon can contour a larger rod R2 or perform other surgical procedureswhile the spine is held by the relatively smaller rod. The relativelylarger rod R2, once prepared as the surgeon desires, can then beinserted into channel 124 of fixation element 110, and locked withanother set screw 144 a.

It will be noted that in the illustrated embodiments of fixationelements 10 and 110, the attachment portion 14, 114 is substantiallycentered between legs 16 and 18. The present invention includesembodiments in which attachment portion 14 may be nearer to one leg oranother, or it may be directly beneath one of channels 22 or 24, or havesome other non-symmetrical configuration.

Turning now to FIG. 5, there is shown a fixation element 210. Fixationelement 210 is similar to fixation element 10, except head portion 212and attachment portion 214 are not initially integral with or fixed toeach other. Rather, attachment portion 214 is separate from head portion212, and is rotatable with respect to head portion 212. Like fixationelement 10, fixation element 210 includes head portion 212 having twochannels 222 and 224. The channels have wall sections 232, 234, 236 and238 that are threaded with threads 240, 242. One of the channels, e.g.channel 222, communicates with a hole H that extends from the top to thebottom of head portion 212. Toward the bottom end of head portion 212, agroove 258 is set, essentially surrounding hole H.

Attachment portion 214 in this embodiment is a bone screw having bonethreads 250 and a head 260, although it will be understood that hookcould be provided on attachment portion 214 instead. Head 260 issubstantially cylindrical, with a flange 262 at the top of head 260, andan internal print 264 within head 260 to enable attachment portion 214to be screwed into a bone.

Fixation element 210 is assembled by inserting head 260 of attachmentportion 214 into hole H of head portion 212 through the bottom end ofhead portion 212. A C-shaped snap ring 266 is provided to retainattachment portion 214 within head portion 212. Snap ring 266 has aninner diameter larger than the diameter of head 260, but smaller thanthe diameter of flange 262 of head 260. The outer diameter of snap ring266, in its non-stressed state, is slightly larger than the diameter ofgroove 258 in head portion 212. Thus, attachment portion 214 isrotatable with respect to head portion 212, but not necessarilymulti-axially moveable with respect to head portion 212.

To use fixation element 210, a hole in a bone (e.g. a vertebra) isprepared as described above. The assembled fixation element 210 is thencoupled to the bone, by inserting the attachment portion 214 into thehole and screwing it into the bone. Attachment portion 214 may bescrewed in to a point where the bottom of head portion 212 contacts boneand flange 262 presses against snap-ring 266, effectively holdingattachment portion 214 with respect to head portion 212. Alternatively,attachment portion 214 can be screwed in to a lesser degree, withrotation of head portion 212 with respect to attachment portion 214being inhibited or prevented by insertion of one or more rods into oneor both channels 222, 224. Once such rod(s) are inserted into one orboth of channels 222 and 224 they are locked therein, as described abovewith respect to fixation element 10.

Referring now to FIG. 6, there is shown an embodiment of a fixationelement 310. Fixation element 310 is very similar to fixation element210, except that attachment portion 314 is configured so that itsconnection with head portion 312 is a multi-axial connection. Apreferred configuration for the connection between head portion 312 andattachment portion 314 is disclosed in U.S. Pat. No. 6,280,445 to Barkeret al., the entirety of which is incorporated by reference. Accordingly,attachment portion 314 includes a rounded head 360 that sits within holeH of head portion 312, and is retained therein by a C-shaped snap ring366 seated in groove 358. A crown member 370 sets atop the head 360 ofattachment portion 314.

Fixation element 310 is connected to a bone in essentially the samefashion as fixation element 210 described above. After attachmentportion 314 is screwed into the bone, head portion 312 may be adjustedmulti-axially with respect to attachment portion 314. A rod isintroduced into channel 322, and any further multi-axial adjustments ofhead portion 312 with respect to attachment portion 314 can be made. Aset screw 344 is threaded into threads 340 communicating with channel322. Locking down set screw 344 presses the rod down on crown member370, which locks head 360 of attachment portion 314 between crown member370 and snap ring 362. In a particular embodiment, head 360 may haveridges 372 that are somewhat harder than the material of crown member370, so that crown member 370 and head 360 are locked together by ridges372 biting into crown member 370.

Referring now to FIG. 7, a further embodiment of a fixation element 410is disclosed. Fixation element 410 includes a head portion 412 and anattachment portion 414. In fixation element 410, head portion 412 andattachment portion 414 may be integral or initially fixed with eachother (as in fixation member 10), rotatable with respect to each other(as in fixation member 210), or multi-axially connected (as in fixationmember 310). Head portion 412 includes an underside 456 having anapproximately anatomically-shaped curvature. In a specific embodiment,the curvature has a concave aspect that approximates the curvature of aside of a vertebra. In another embodiment, the curvature may have aconcave aspect in a first cross-section and a convex aspect in a secondcross-section, e.g. one perpendicular to the first cross-section.Extending from surface 456 is a prong or spike 474. Spike 474 isintended to be inserted into the bone tissue when fixation element 410is attached to a bone, to provide yet further stability to the implantconstruct. In other respects, fixation element 410 can have any of thefeatures or attributes of fixation elements 10, 110, 210, and/or 310.

Referring now to FIG. 8, fixation element 510 in yet another embodimentis disclosed. Fixation element 510 may include attributes or featuresfrom any of fixation elements 10, 110, 210, and/or 310, wherein anattachment portion 514 is not centered with respect to head portion 512,or is beneath one channel (e.g. channel 522) of head portion 512. Inaddition, fixation element 510 includes a second attachment portion 514a connected to head portion 512. In a specific embodiment, head portion512 can include a hole H′ communicating with channel 524 and extendingfrom bottom surface 556 through head portion 512. Attachment portion 514a can be similar to attachment portion 214 or 314, in which case thefeatures of fixation elements 210 and/or 310 providing for connectionbetween the respective attachment portions and head portions would beincluded in fixation element 510. Alternatively, attachment portion 514a may be a standard bone screw with a curvate head 562 and an internalprint 564, that could rest against the lower edge of the hole H′. Inthat case, an additional hole 580 may be provided that communicates withhole H′, and is threaded to accommodate a set screw (not shown) therein,which can lock attachment portion 514 a within hole H′ in a desiredorientation.

Fixation element 510 is attached to a bone in substantially the samefashion as described above, except an additional hole must be drilled ina bone to accommodate attachment portion 514 a. As one example,attachment portion 514 can be threaded into the bone, and attachmentportion 514 a can then be threaded into the second hole in the bone andused to make adjustments in the positioning of fixation element 510 withrespect to the bone. One or more rods may be inserted in channels 522and 524, and fixation element 510 locked with respect to the rods bythreading set screws down on them, as described above.

Referring now to FIG. 9, there is shown an embodiment 610 of a fixationelement. Fixation element 610 has a U-shaped head portion 612 with asingle channel 622 therethrough, and is connected to an attachmentportion 614 which in a specific embodiment is a threaded screw portion.Walls 632 and 634 of channel 622 include threads 640 for accommodating aset screw 644. Walls 632 and 634 are of a height that enables insertionof two separate rods within channel 622 of head portion 612. Thus, for afixation element 610 intended to accommodate two rods of 5.5 mmdiameter, the height of walls 632 and 634 would be at least 11 mm plusthe height of set screw(s) 644. With reference to FIG. 9, rod R1 isplaced within channel 622, followed by a set screw 644, screwed intothread 640. A second rod R2 would be placed atop set screw 644, and asecond set screw 644 would be threaded into threads 640 to lock thesecond rod R2 with respect to head portion 612.

The diameters of rods R1 and R2 could be equal or they may be differentto provide adjustability and stability prior to final locking down asdescribed above. It will also be noted that a configuration of headportion 612 to accommodate two rods may be combined with a multi-axialhead portion/attachment portion connection (such as those shown in U.S.Pat. No. 5,797,911 to Sherman et al. and 6,280,445 to Barker et al., theentireties of which are incorporated herein by reference), or could berotational with respect to each other as shown above with respect tofixation member 210. Further, although channel 622 is shown as extendingfrom a back or proximal surface of head portion 612 toward attachmentportion 614, it will be understood that channel 622 could extendlaterally, i.e. from a side surface of head portion 612 toward anopposite side surface. Two rods or other elongated members could then beinserted into channel 622 from the side and fixed with respect to headportion 612 substantially as described above, or as described furtherbelow with respect to FIGS. 10 and 11.

Yet a further embodiment is shown in FIG. 10. A fixation element 710 isprovided with a head portion 712 and an attachment portion 714. In thisembodiment, head portion 712 has channels 722 and 724. Channel 722, likechannel 22 in FIG. 1, is substantially straight, extends through headportion 712, and is open to the back (i.e. the portion oppositeattachment portion 714) of head portion 712. Channel 724 is alsosubstantially straight and extends through head portion 712, but channel724 opens to the side of head portion 712. Thus, head portion 712 hasone channel that is “back-loading” for one elongated member (e.g. rod R1in FIG. 4 or 9) and “side-loading” for another elongated member (e.g.rod R2 in FIG. 4 or 9).

Head portion 712 may also include a hole 782 from the back of headportion 712 to channel 724. Hole 782 may be internally threaded andaccommodate a set screw 784, which is used to lock a rod within channel724. In one embodiment, set screw 784 has a threaded portion 786, andmay also have a conically-shaped or tapered end portion 788. It will beunderstood that any of several types of holder or locking member,including a set screw 744 (threaded into hole 782 or into channel 724from the side of head portion 712) or other holder(s) described above,can be used. Channel 722 is configured to accommodate a holder such asset screw 744 or other holder(s) described above.

Head portion 712 is shown in this embodiment to be fixed with respect toattachment portion 714, with attachment portion 714 substantially in themiddle of head portion 712. Of course, attachment portion 714 may berotatably or multi-axially connected to head portion 712, or locatedtoward one side of head portion 712, or multiple attachment portions 714may be provided, as described in detail above.

Another embodiment of a fixation element 810 is shown in FIG. 11.Fixation element 810 is much like fixation element 710, with theexception that both channels 822 and 824 are open to the sides of headportion 812 of fixation element 810. In one particular embodiment, holes882 a and 882 b are provided to communicated with channels 822 and 824.Holes 882 a and 882 b may be internally threaded (as described above) toaccommodate set screws such as 884 a and 884 b, or may be configured toaccommodate alternative holders, as described above. As with fixationelement 710, attachment portion 814 of fixation element 810 may berotatably or multi-axially connected to head portion 812, or locatedtoward one side of head portion 812, or multiple attachment portions 814may be provided, as described in detail above.

The implants described above are preferably made from a biocompatiblematerial such as stainless steel, titanium, plastics or other sturdybiocompatible and/or resorbable materials. The elongated members may beflexible or rigid rods, cables or similar items. It is envisioned thatwell-known open and minimally-invasive surgical procedures may be usedto implant embodiments of the present invention.

The size of the implants described above may be identical or similar toimplants currently used in spinal and other orthopedic surgeries. It hasbeen found that the implants described above may have particularapplication to smaller vertebrae or other bones (e.g. those in childrenor other small persons, or adult cervical vertebrae), since one implantattaching to a bone can accommodate two rods or other elongated members.Accordingly, these implants may be made in standard and smaller sizesfor such uses.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected. For example, while the embodimentsdescribed above have two channels (e.g. channels 22 and 24) foraccommodating longitudinal supports, the present invention contemplatesfixation elements with head portions having a larger number of channelsor that can accommodate more than two rods or other support members.Further, it will be seen that aspects of one embodiment described abovecan be incorporated into another of the embodiments. For example, the“stacked rod” feature of fixation element 610 could be included withfixation element 10. In that case, one of the channels of fixationelement 10 would be of a height sufficient to place one rod atop anotherin that channel, as described with respect to fixation element 610.Still further, it will be seen that the channel or channels may bedifferently oriented, as for example opening to the side of the headportion.

1-35. (canceled)
 36. A fastening system comprising: a head portioncomprising a first channel and a second channel that is spaced apartfrom the first channel, the head portion comprising an inner surfacedefining a hole; and an attachment portion comprising a bone-engagingportion and a head rotatably disposed in the hole such that the headportion is rotatable relative to the attachment portion in a pluralityof planes.
 37. A fastening system as recited in claim 36, wherein thehole is positioned between the first and second channels.
 38. Afastening system as recited in claim 36, wherein the hole is positionedbelow one of the first and second channels.
 39. A fastening system asrecited in claim 36, wherein the first channel extends parallel to thesecond channel.
 40. A fastening system as recited in claim 36, whereinthe first channel extends to the top of the head portion and the secondchannel extends to a side of the head portion.
 41. A fastening system asrecited in claim 36, wherein the head comprises an internal printconfigured to engage a tool to rotate the attachment portion about anaxis defined by the attachment portion.
 42. A fastening system asrecited in claim 36, further comprising a retaining member disposed inthe hole that engages an outer surface of the head to prevent the headfrom falling out of the hole.
 43. A fastening system as recited in claim36, wherein the head portion comprises a first leg, a second leg and athird leg positioned between the first and second legs, the first legand a first surface of the third leg defining the first channel, thesecond leg and a second surface of the third leg defining the secondchannel, wherein the first leg and the first surface comprise threadsthat face one another and the second leg and the second surface comprisethreads that face one another.
 44. A fastening system as recited inclaim 36, wherein: a first inner surface of the head portion defines thefirst channel and a second inner surface of the head portion defines thesecond channel, the first and second inner surfaces comprising a firstthread form; and the fastening system comprises at least one retainingmember including a second thread form configured to engage the firstthread form.
 45. A fastening system as recited in claim 36, wherein: aninner surface of the head portion defines the first channel, the innersurface comprising a first thread form; the fastening system furthercomprises an elongated member positioned in the first channel; and thefastening system further comprises a retaining member including a secondthread form configured to engage the first thread form such that an endface of the retaining member engages the elongated member to retain theelongated member in the first channel.
 46. A fastening system as recitedin claim 36, further comprising a crown member positioned between aninner surface of the head portion that defines the hole and the head.47. A fastening system as recited in claim 36, further comprising acrown member positioned between an inner surface of the head portionthat defines the hole and the head, wherein the crown comprises aconcave surface that engages a convex surface of the head.
 48. Afastening system as recited in claim 36, further comprising a crownmember positioned between an inner surface that defines the hole and thehead, the head comprising ridges that are harder than the crown membersuch that the head is configured to be locked to the crown member by theridges biting into the crown member.
 49. A fastening system as recitedin claim 36, wherein the head portion comprises an aperture extendingbetween the first and second channels configured for disposal of a tool,the aperture being parallel to an axis defined by the head portion. 50.A surgical method comprising: providing the fastening system recited inclaim 36; engaging the bone-engaging portion with a bone of a patient;positioning a first elongated member in the first channel; andpositioning a second elongated member in the second channel.
 51. Amethod as recited in claim 50, wherein positioning the first elongatedmember in the first channel comprises rotating the head portion relativeto the attachment portion such that the first elongated member isaligned with the first channel and translating the first elongatedmember relative to the head portion.
 52. A fastening system comprising:a head portion comprising a U-shaped first channel and a U-shaped secondchannel that is spaced apart from the first channel and extends parallelto the first channel, the head portion comprising an inner surfacedefining a hole; an attachment portion comprising a bone-engagingportion and a head rotatably disposed in the hole such that the headportion is rotatable relative to the attachment portion in a pluralityof planes; a cylindrical first rod configured to be positioned in thefirst channel; a cylindrical second rod configured to be positioned inthe second channel; a first set screw configured to threadingly engagethe first channel such that an end surface of the first screw engagesthe first rod to retain the first rod in the first channel; and a secondset screw configured to threadingly engage the second channel such thatan end surface of the second set screw engages the second rod to retainthe second rod in the second channel.
 53. A fastening system as recitedin claim 52, wherein: the hole is positioned between the first andsecond channels; and the system further comprises a retaining memberdisposed in the hole that engages an outer surface of the head toprevent the head from falling out of the hole.
 54. A fastening system asrecited in claim 52, wherein: the hole is positioned below one the firstand second channels; and the system further comprises a crown memberpositioned between the inner surface of the head portion that definesthe hole and the head, wherein the crown comprises a concave surfacethat engages a convex surface of the head.
 55. A fastening system asrecited in claim 52, further comprising a crown member positionedbetween the inner surface that defines the hole and the head, the headcomprising ridges that are harder than the crown member such that thehead is configured to be locked to the crown member by the ridges bitinginto the crown member.